Process for extruding a metal section

ABSTRACT

In a process for the manufacture of a shaped bar consisting of an at least partially metallic material, a preform is shaped to form the shaped bar in the partially solid/partially liquid state and the shaped bar in the partially solid/partially liquid state is guided through a chilled mould for setting. An optionally heatable preform chamber is provided for receiving the preform, an optionally heatable forming chamber is connected to the preform chamber for shaping the preform to form the shaped bar, and a chilled mold is connected to the forming chamber for the setting of the shaped bar. A die can optionally be arranged immediately downstream of the mould for the final shaping process and the device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a process for the manufacture of a shaped bar.The invention also covers a device suitable for carrying out theprocess, as well as use of the process and use of the device.

2. Discussion of the Prior Art

One known process for the manufacture of metal profiles is extrusion.However, with current extrusion technology, it is very difficult tomanufacture large Aluminium alloy profiles with a width of more thanapproximately 700 mm. Another disadvantage consists in that it is verydifficult to obtain profile wall thicknesses of less than approximately2 mm. However, in view of weight and cost savings, it would be highlydesirable to reduce the wall thicknesses of profiles, i.e. to achieveall thicknesses of less than 1 mm while still observing the usualgeometric profile tolerances.

The limited extrusion force and the limited possibilities of obtaininguniform metal distribution with respect to, temperature and flow rateare the essential factors preventing the manufacture of extremelythin-walled profiles using current extrusion technology.

However, in current extrusion technology, certain limits exist even inthe manufacture of profiles of medium or small width, with respect tothe materials than can be processed and the cross-sectional dimensionsto be produced. For example, it is virtually impossible or verydifficult to press hard Aluminium alloys with the extrusion forcesnormally used in conventional extruders. This limitation applies inparticular to the manufacture of hollow profiles, particularlymulti-compartment hollow profiles. The resulting slow extrusion rate hasa negative effect on production costs. In addition, the dimensionaltolerances are often insufficient and there is often poor mentaldistribution, noticeable above all through insufficient mould filling inshaped parts with small metal crossectional dimensions.

The extrusion of particle-reinforced composite materials consisting of ametal matrix with particles of fibres of non-metallic, high-meltingmaterials dispersed therein leads to comparable problems to theabove-mentioned processing of hard alloys. The manufacture of theseso-called Metal Matrix Composites is described in detail inWOA-87/06624, WOA-91/02098 and WOA-92/01821. The particles to beintroduced into the metal matrix are first essentially introducedhomogeneously in an alloy melt and the molten composite material is thencase, e.g. by continuous casting, into the format suitable for furtherprocessing by extrusion of rolling.

A process of the type mentioned at the outset is known fromJP-A-04066219. The aim of the invention is therefore to provide aprocess of the type mentioned at the outset and a device suitable forcarrying out the process, by means of which hard alloys and compositematerials of all types can be processed into high-quality products in acost-effective manner. Another aim is the economical manufacture ofextremely thinwalled large profiles and/or large profiles of extremewidth. In addition, it should be possible to modify existing extrusioninstallations in a simple and cost-effective manner.

Pursuant to the present invention, preform is usually inserted in theform of billet into a preform chamber which will be described in moredetail hereinbelow. The preform and the preform chamber thereforecorrespond to the extrusion billet and the container in extrusion.

By virtue of the fact that the preform is shaped in the partiallysolid/partially liquid state according to the invention, materials whichwere virtually impossible to manufacture of could only be manufacturedin a very uneconomical manner by conventional extrusion can be processedinto profiles with a constant extrusion force. As a result of the lowextrusion forces required, comparable profile dimensions can be pressedin smaller installations than in the case of conventional manufacturingmethods, this being advantageous from the point of view of productioncosts.

One essential advantage of the process according to the invention isthat hard alloys and composite materials can be processed into profileswith metallurgical properties that cannot be obtained by conventionalextrusion.

Wider profiles with smaller profile wall thicknesses than in possiblewith current extrusion technology can also be manufactured by theprocess according to the invention.

The central idea underlying the process according to the inventionconsists in bringing the preform so close to the final cross sectionwith the lowest possible extrusion force that the final shaping of thecross section of the shaped bar can also be carried out with lowextrusion force by means of a die. This is achieved by the shaping inthe partially solid/partially liquid state according to the invention.

Compared to the use of conventional perfectly set extrusion billets, theuse of preforms in the partially solid/partially liquid state has theadvantage that shaping can be carried out with substantially lowerextrusion force. If the liquid phase fraction is kept low compared tothe solid phase fraction, sufficiently rapid setting can also beachieved in thick-walled profile regions.

As the pressure applied to the preform, i.e. the extrusion force, cannotbe increased as desired, e.g. as a result of the high containertemperature of up to 600° C. required in the case of special additives,in an advantageous development of the process according to theinvention, the preform is pressed to form the shaped bar with the aid ofa tensile force acting on the shaped bar.

The degree of shaping upon the transition of the preform to the shapedbar in the partially solid/partially liquid state is preferably at least50%, preferably at least 80%. The degree of shaping refers here to thereduction in the cross section during the shaping of the preform to formthe shaped bar.

If the shaped bar has to have a high surface quality and/or highdimensional tolerance, the shaped bar can be guided through a dieimmediately after it emerges from the mould for the final shaping of thecross section of the shaped bar. This final shaping of the cross sectionof the shaped bar is advantageously carried out with shaping of no morethan 15%, preferably no more than 10%.

After it emerges from the mould or the die, the shaped bar is preferablycooled by the complete evaporation of a coolant sprayed on to the shapedbar. Cooling with complete evaporation of the coolant prevents liquidcoolant from being able to flow back in the direction of the hot metalpossibly still in the partially liquid state. By virtue of this measure,the cooling means can be arranged as close as possible to the site ofthe desired cooling, i.e. as close as possible to the mould or the die.

The liquid phase fraction in the preform during the shaping thereofdepends on the nature of the material to be processed. In general, thisfraction is no more than 70%, and is preferably approximately 20 to 50%.In principle, any materials in which a partially solid/partially liquidstate can be set within a sufficiently broad temperature interval forpractical purposes can be used for the preforms. Examples of suitablematerials are:

alloys, in particular aluminium and magnesium alloys in the thixotropicstate, with different solid/liquid fractions, e.g. hard alloys of theAlMg or MgAl type,

alloys based on magnesium or copper in the thixotropic state, withdifferent solid/liquid fractions, and

alloys based on aluminium or magnesium with metallic or non-metallicfractions of high-melting particles and/or fibres (Metal MatrixComposites).

Aluminium and magnesium alloys in particular are suitable as the metalmatrix. Its basic properties, such as mechanical strength and elongationcan be achieved in a known manner by means of the various types ofalloy. The non-metallic additives can have an advantageous effect, interalia, on hardness, rigidity and other properties. Preferred non-metallicadditives are ceramic materials such as metal oxides, metal nitrides andmetal carbides. Examples of materials of this kind are silicon carbide,aluminium oxide, boron carbide, silicon nitride and boron nitride.

In principle, profiles can be manufactured from composite materials insuch a manner that the preform already contains all of the materials inthe desired form. However, with the process according to the invention,a filler material can also be added to the preform in the partiallysolid/partially liquid state before it enters the mould. This fillermaterial can be added indifferent forms and in different states ofaggregation. E.g. the filler material can be supplied continuously tothe preform in solid form as wire, fibres or powder. Wires, e.g. in theform of reinforcements can remain in the profile. However, a materialwhich melts in the partially liquid/partially solid range, where it thenalloys or triggers a chemical reaction can also be added in the form ofwire. The filler material can also be added in the liquid state or inthe gaseous state.

One essential advantage of the process according to the invention overconventional extrusion also consists in that preforms can be composed ofcross-sectionally different material regions. E.g., the edge zone oreven internal parts of a profile can be provided with differentmechanical properties from those of the matrix, such as higher hardness,rigidity, abrasion resistance and the like.

Preforms with cross-sectionally different material regions can beprocessed in that the preform is guided through a heating zone before itis shaped to form the shaped bar and is set to a uniform solid/liquidratio over the entire cross section of the shaped bar in the heatingzone. To this end, a cross-sectionally different temperature profile canbe set in the heating zone as a function of cross-sectionally differentmaterial regions.

A device suitable for carrying out the process according to theinvention includes an optionally heatable preform chamber for receivingthe preform, an optionally heatable forming chamber connected to thepreform chamber for shaping the preform to form the shaped bar, and achilled mould connected to the forming chamber for the setting of theshaped bar, wherein a die can optionally also be arranged immediatelydownstream of the mould for the final shaping of the cross section ofthe shaped bar.

An extractor means can be arranged downstream of the downstream of thedevice according to the invention in order to apply a tensile force tothe shaped bar and therefore to assist the entire extrusion process. Theextractor means can include grippers and/or drive rollers.

The wall of the forming chamber preferably passes over into the wall ofthe mould with a constant curvature, i.e. the cross section of thepreform being shaped to form the shaped bar decreases continuously.

Heating lines are arranged in the preform chamber and/or in the formingchamber in order to produce or maintain the partially solid/partiallyliquid state of the preform. In addition, an intermediate layer of aheat-insulating material is advantageously arranged between thegenerally heated forming chamber and the chilled mould.

A heating means is advantageously arranged between the preform chamberand the forming chamber. This heating means preferably has individuallyheatable flow channels for the preform.

In a preferred embodiment of the device according to the invention, theheating means consists of at least two disc-shaped heating elementsarranged side by side and provided with integrated heating conductors,the heating elements being individually controllable.

A direct cooling means is provided for further cooling of the shaped baremerging from the mould or the die. For the aforementioned reasons, acooling means with complete evaporation of the coolant applied to theshaped bar is preferred.

A particularly preferred application of the process and device accordingto the invention consists of the manufacture of profiles withcross-sectionally different material regions.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features and details of the invention will be clearfrom the following description of preferred embodiments and withreference to the accompanying diagrammatic drawings, in which:

FIG. 1 is a diagrammatic representation of a device for the manufactureof a shaped bar;

FIGS. 2 to 4 are longitudinal and cross sections through differentpreforms with cross-sectionally different material regions;

FIG. 5 is a top view of a disc-shaped heating element;

FIG. 6 is a partial cross section through the heating element of FIG. 5along the line of I—I thereof;

FIG. 7 is a longitudinal section through a heating means with heatingelements;

FIG. 8 is a temperature profile over the length of the heating means ofFIG. 7, and

FIG. 9 shows another embodiment of a heating means with heatingelements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to FIG. 1, an extrusion installation (not shown in thedrawings for the sake of clarity) for the manufacture of metal profileshas a container 10 with a preform chamber 12 for receiving preforms 36.A heating means 42, a forming chamber 14, a mould 16 and a die 18 areconnected to the preform chamber 12 in the aforesaid order as viewed inthe extrusion direction x.

The preform chamber 12 and the forming chamber 14 are provided withheating lines 20, 21 for heating the two chambers 12, 14. The heatingmeans 42, has a plurality of individually heatable flow channels 44arranged parallel to the extrusion direction x for heating the preform36 to a state of equilibrium with respect to the desired solid/liquidratio. An intermediate layer 15 of a heat-insulating material isarranged between the forming chamber 14 and the mould 16.

The mould 16 is provided with a first cooling means 24 for indirectcooling of the metal bar setting by contact with the mould wall 26. Asecond cooling means 30 is arranged within the die 18 and serves fordirect cooling of the shaped bar 40 emerging from the die by the directapplication of coolant thereto.

As in the case of extrusion, the profile chamber 14 can be provided witha corresponding mandrel insert for the manufacture of hollow profiles.

An inlet channel 46 for supplying a filler material 48 into thepartially solid/partially liquid region opens into the forming chamber14. This filler material 48 can be supplied in solid form as wire,fibres or powder, in the liquid state, or even in the gaseous state.

An extractor means 64 is arranged at the outlet end of the die 18. Atensile force K is applied in the extrusion direction x to the shapedbar 40 emerging from the die in 18 by means of drive rollers 66. Thismeasure removes pressure from the extrusion process so that anacceptable extrusion rate can be achieved even at elevated extrusiontemperatures.

The method of operation of the arrangement described hereinbefore willnow be described in more detail with reference to the diagrammaticrepresentation illustrated in the drawings. For the sake ofcompleteness, it should also be mentioned here that the arrangementaccording to the invention is designed in such a manner that it can beinstalled in a problem-free manner in a conventional extrusioninstallation.

The preform 36 in the form of a metal billet which is usually alreadypreheated is introduced into the preform chamber 12 and is heatedfurther by means of the heating lines 20. The preform 36 is driven inthe extrusion direction x by means of a punch 32 with a dummy block 34and is converted into the desired partially solid/partially liquid statewithin the heating means 42. The main part of the shaping of the preform36 is effected in the forming chamber 14, the wall 22 of the formingchamber 14 continuously moving further towards the inlet opening of themould 16.

The setting of the metal bar from the partially solid/partially liquidstate f/f1 to the solid state f is effected within the mould 16, thedesign of which essentially corresponds to that of a conventionalcontinuous casting mould, along a setting front 38 departing from themould wall 26. Immediately after it emerges from the mould 16, the setmetal bar enters the die 18, where final shaping is effected in a dieopening 28.

The shape of the shaped bar 40 within the mould 16 is ideally alreadyalmost such that only a small change in the cross section or slightshaping is still effected in the die 18, i.e. the die 18 servesprincipally for the formation of a high-quality profile surface and theproduction of a dimensionally accurate profile cross section. The directapplication of coolant from the cooling means 30 to the shaped bar 40emerging from the die 18 ensures that any partially liquid fractionsstill remaining in the interior of the profile are set completely. Afterit emerges from the die 18, the set shaped bar 40 is gripped by thedrive rollers 66 of the extractor means 64 and is drawn out of the die18 in the extrusion direction x.

In addition to pure metal alloys, metals with metallic or non-metallicadditives having a higher melting point than the basic metal are alsosuitable as materials for the preform 36 to be supplied to the preformchamber 12. These materials include, e.g. particle-reinforced orfibre-reinforced materials with an aluminium matrix, i.e. so-calledMetal Matrix composites. Other suitable materials are alloys, inparticular aluminum alloys, in the thixotropic state, as well asnon-thixotropic hard alloys, e.g. AlMg alloys, in particular alloys witheutectic solidification.

Various preforms 36 with cross-sectionally different material regions A,B, C, D are shown by way of example in FIGS. 2 to 4. It will beimmediately clear that profiles with cross-sectionally differentmaterial properties can be produced with these preforms. A temperatureprofile cross-sectionally adapted to the respective material regionswithin the heating means 42 can ensure that a uniform solid/liquid ratiois set in all of the material regions A, B, C, D at the outlet of theheating means 42.

The preforms 36 can essentially be supplied to the preform chamber 12already in the partially solid/partially liquid state. However, in viewof the fact that it is easier to manipulate perfectly rigid preforms,the latter are usually heated to just below the respective lowestsolidus temperature and are only converted to the desired partiallysolid/partially liquid state once they are inside the preform chamber 12and the forming chamber 14.

In the following tables, the values for the pressure p and the degree ofshaping d determined for one possible arrangement by way of a modelcalculation are associated with the individual shaping stations of thearrangement according to the invention.

preform chamber forming chamber mould die p (bar) 100 500 100 1000 d (%)0 90 2 8

According to FIGS. 5 to 7, the heating means 42 is composed ofindividual disc-shaped heating elements 50. These heating elements 50made, e.g. of steel, have openings 52 surrounded by grooves 54 workedinto the surface. After the insertion of heating wires 56, the grooves54 are closed by welding. FIG. 7 shows the alignment of disc-shapedheating elements 50 relative to the heating means 42. The openings 52 inthe individual disc-shaped heating elements 50 are adapted to oneanother in such a manner that they form the through flow channels 44.

FIG. 8 shows the percentage liquid fraction of the material to beprocessed over the length of the heating means 42 of FIG. 7. Atemperature profile leading to a substantially linear increase in theliquid phase fraction is produced by individual control of theindividual heating elements 50. When the material to be processed entersthe heating means 42, the liquid phase fraction is, e.g. 20%, and at theoutlet end of the heating means it is, e.g. 60%. In the case of aheating capacity of approximately 1 kW per heating element, 5 to 6elements are sufficient to produce the desired liquid phase fraction.

FIG. 9 shows an alternative embodiment of the heating means 42.Disc-shaped heating elements 58, e.g. of boron nitride have heatingconductors 60 integrated into their surface. The thickness of theheating elements 58 is, e.g. 1 mm. The individual heating elements 58are separated from one another by intermediate discs 62, e.g. of carbonfibre-reinforced graphite. The heating elements 58 and the intermediatediscs 62 have openings 52 which in their entirety form the flow channels44. A heating means of this kind can be operated at temperatures inexcess of 1000° so that the liquid phase fraction can already be set toapproximately 20% by reflecting heat into the preform 36 before itenters the heating means 42. In addition, a desired temperature profilecan be set substantially more rapidly and more precisely by this means.

What is claimed is:
 1. A process for manufacturing a shaped bar from apartially solid/partially liquid preform including an at least partiallymetallic material, comprising the steps of: initially guiding thepreform through a plurality of heatable parallel flow channels of aheating zone for heating the preform and setting the preform to auniform solid/liquid ratio over an entire cross-section of the shapedbar in the heating zone; pressing the preform in the partiallysolid/partially liquid state through a shaping opening to form theshaped bar; and guiding the shaped bar in the partially solid/partiallyliquid state through an open-ended chilled mold for solidification.
 2. Aprocess according to claim 1, wherein the shaping step includes pressingthe preform to form the shaped bar using a tensile force acting on theshaped bar.
 3. A process according to claim 1, wherein the shaping stepincludes shaping the preform by at least 50%.
 4. A process according toclaim 3, wherein the shaping step includes shaping the preform by atleast 80%.
 5. A process according to claim 1, and further comprising thestep of final shaping a cross-section of the shaped bar in a dieimmediately after the shaped bar emerges from the mold.
 6. A processaccording to claim 5, wherein the step of final shaping of thecross-section of the shaped bar includes shaping of no more than 15%. 7.A process according to claim 6, wherein the final shaping step includesshaping of no more than 10%.
 8. A process according to claim 1, andfurther comprising the step of cooling the shaped bar after it emergesfrom the mold by complete evaporation of a coolant sprayed onto theshaped bar.
 9. A process according to claim 5, and further comprisingthe step of cooling the shaped bar after it emerges from the die bycomplete evaporation of a coolant sprayed onto the shaped bar.
 10. Aprocess according to claim 1, wherein the shaping step includes shapingthe preform with a liquid phase fraction of at most 70%.
 11. A processaccording to claim 10, wherein the shaping step includes shaping thepreform with a liquid phase fraction of 20 to 50%.
 12. A processaccording to claim 1, wherein the preform includes a thixotropic alloy.13. A process according to claim 12, wherein the preform includes one ofa thixotropic aluminium alloy and a thixotropic magnesium alloy.
 14. Aprocess according to claim 1, wherein the preform is a non-thixotropichard alloy of one of aluminium and magnesium.
 15. A process according toclaim 14, wherein the preform is one of an AlMg alloy and an MgAl alloy.16. A process according to claim 1, wherein the preform is one of areinforced aluminium material and a reinforced magnesium material, andreinforced material being one of particle-reinforced andfiber-reinforced.
 17. A process according to claim 1, wherein thepreform is composed of cross-sectionally different material regions. 18.A process according to claim 1, and further comprising the step ofadding a filler material to the preform in the partially solid/partiallyliquid state before it enters the mold.
 19. A process according to claim18, wherein the step of adding filler material includes adding thefiller material in solid form as one of wire, fibers and powder.
 20. Aprocess according to claim 18, wherein the step of adding fillermaterial includes adding a liquid filler material.
 21. A processaccording to claim 18, wherein the step of adding filler materialincludes adding a gaseous filler material.
 22. A process according toclaim 1, wherein the preform is composed of cross-sectionally differentmaterial regions and the step of guiding the preform through a heatingzone includes setting a cross-sectionally different temperature profilein the preform in the heating zone as a function of thecross-sectionally different material regions.
 23. A device formanufacturing a shaped bar from a preform of at least partially metallicmaterial, comprising: a heatable preform chamber for receiving thepreform; a heatable forming chamber connected to the preform chamber forshaping the preform in a partially solid/partially liquid state to formthe shaped bar; an open-ended chilled mold connected to the formingchamber for solidifying the shaped bar; and heating means having aplurality of heatable parallel flow channels for heating the preform,the heating means being arranged between the preform chamber and theforming chamber.
 24. A device according to claim 23, and furthercomprising extractor means arranged downstream of the shaped bar forapplying a tensile force thereto.
 25. A device according to claim 23,and further comprising die means arranged immediately downstream of themold for final shaping a cross-section of the shaped bar.
 26. A deviceaccording to claim 23, wherein the forming chamber has a wall thatpasses over into a wall of the mold with a constant curvature.
 27. Adevice according to claim 23, and further comprising heating linesarranged in at least one of the preform chamber and the forming chamber.28. A device according to claim 23, and further comprising anintermediate wall of a heat-insulating material arranged between theforming chamber and the mold.
 29. A device according to claim 24,wherein the flow channels are individually heatable.
 30. A deviceaccording to claim 29, wherein the heating means includes at least twodisc-shaped heating elements arranged side by side and provided withintegrated heating conductors, the heating elements being individuallycontrollable.
 31. A device according to claim 23, and further comprisingdirect cooling means for further cooling of the shaped bar emerging fromthe mold.
 32. A device according to claim 31, wherein the direct coolingmeans is operative to apply coolant to the shaped bar to an extentsufficient to obtain complete evaporation of the coolant.
 33. A deviceaccording to claim 25, and further comprising direct cooling means forfurther cooling of the shaped bar emerging from the die means.